For this type of a shutdown, I would seriously consider having the (M) go to 145th Street-8th Avenue OR (once the SAS opens) 96th/2nd on weekends UNLESS the (M) can run its regular weekday route on weekends while Queens Boulevard work goes on.

57th/6th is not ideal for a long-term terminal (even on weekends) due to the (F) using that as a through station.